280 ECHINODERMATA— ECHINOZOA phylum iv 



than one large periproctal plate. Oculars all .exsert or one to all insert, 



Acrosalenia hemicidaroides Wright. Middle Jura ; Stanton, Wiltshii 



of test, Vi (fifter Wright). 



Dorsal, lateral and ventral aspeets 



commonly I, Y insert. Spines cylindrical, striated or piain. Represented 

 by numerous species from the Lias to the Lower Cretaceous. 



Family 2. Phymosomatidae Meissner. 



Ämbulacral plates Compound. Primordial interambulacral plates resorbed. 

 Oculars becoming insert in the sequence I, F, IV, II, III. Periproct with 

 numerous small plates only. Primary tubercles imperforate. Spurs from pyramids 

 Support the teeth dorsally. Jura to Recent. 



Cyphosoma Agassi z (Fig. 394). 



Fig. 394. 



Cyphosoma hoeniui Mantell. White Chalk 

 Sussex. Ventral aspect, '/i- 



Test depressed, with few coronal plates. 

 Amb with well-developed poriferous areas 

 undulating. Pore-pairs biserial at the 

 apex, crowded at the peristome. lAmb 

 broader than the Amb, with two or more 

 vertical rows of primary tubercles, which 

 are imperforate and crenulate, like those 

 of the Amb. Apical systcm encroaching 

 upon the posterior lAmb. Jura to Ter- 

 tiary. 



Glyptocidaris A. Agassiz. Recent. This 

 genus shows the character of pyramidal 

 spurs given as a family character. 



Micropsis Cotteau. Amh with three to 

 five elements to a Compound plate, and 

 two or more vertical rows of small primary 

 tubercles, which are perforate and crenu- 

 late. Cretaceous and Eocene. 



Family 3. Stomopneustidae Mortensen. 



Ambidacral plates Compound, composed of three elements each, at the mid-zone 

 every four or five ämbulacral plates are boand together and grown over by one 

 primary tubercle. Primordial interambulacral plates and base of corona resorbed. 

 Oculars becoming insert in the sequence 1, V, IV. Periproct with many small plates 

 only. Primary tubercles imperforate. Spurs from pyramids support the teeth 

 dorsally. 



